Desorption in catalysis refers to

• A. The surface area of the catalyst increases
• B. The reactants are activated on the surface
• C. The catalyst is deactivated by adsorption
• D. The products leave the catalyst surface

Answer: (D)

Desorption is the step where product molecules detach from the catalyst surface after the reaction, freeing the active sites for new reactant molecules to adsorb and react. This detachment is essential for turnover: without products leaving the surface, sites would remain blocked and the catalyst couldn’t continue to catalyze more reactions.

In many catalytic processes, reactants first adsorb onto the surface and are activated there, then transform into products that remain bound for a moment before finally desorbing. Desorption is distinct from adsorption and activation, which are about getting reactants onto the surface and into reactive forms, and it’s also distinct from catalyst deactivation by adsorption, which describes species binding too strongly and poisoning the surface. The idea that desorption equals an increase in surface area isn’t correct, since surface area affects how many sites are available, not the step of a product leaving the surface.